1. Field of the Invention
The present invention relates to a shock absorber, and more particularly, to a shock absorber that can improve a ride comfort by reducing a damping force over periods from an ultra-low-speed period to a high-speed period, and can achieve the compact configuration and the cost reduction by reducing the overall length of the processing portion.
2. Description of the Related Art
Generally, a shock absorber is designed to support a weight of a vehicle body and suppress and dampen a vibration transferred from a road surface to the vehicle body, contributing to improving a ride comfort and protecting loaded goods and various parts of a vehicle.
Such a shock absorber includes a cylinder filled with a working fluid (oil), a reciprocating piston rod connected to a vehicle body, and a piston valve connected to a lower end of the piston rod to slide within the cylinder and control a flow of the working fluid.
The existing shock absorber forms one passage within the cylinder by the piston valve. However, this structure has difficulty in increasing a cross-sectional area of the passage and has a limitation in reducing a damping force in a high-speed period.
In addition, in the existing shock absorber, a rapid variation in the damping force occurs at a blow-off point, causing a degradation in ride comfort.
There is known a shock absorber employing a piston valve forming two passages in order to overcome the limitation of the structure where one passage is formed.
However, in the case of the shock absorber provided with the piston valve forming two passages, since a plurality of parts are stacked in the piston valve, the length of processing portions is increased, resulting in an increase in the total height of the apparatus.
In the case of the shock absorber provided with the piston valve forming two passages, a tuning factor is deficient in an ultra-low-speed period, and therefore, there is no margin for tuning.
In addition, the shock absorber provided with the piston valve forming two passages cannot indefinitely increase the diameter of holes forming a compression and rebound passage of the piston valve. Thus, there is a limitation in implementing a degressive characteristic at a high-speed period.
In particular, a shock absorber including a piston valve having a pilot valve mounted with a rubber sealing has a problem in that a ride comfort is degraded by a damping force leg phenomenon that the pilot valve is not closed due to a tension of the rubber sealing during a compression stroke.